National Geologic Map Database
Geologic Unit: Tracy Creek
Map showing publication footprint
  • Usage in publication:
    • Tracy Creek andesite*
  • Modifications:
    • Original reference
  • Dominant lithology:
    • Breccia
    • Andesite
  • AAPG geologic province:
    • San Luis basin

Cross, Whitman, and Larsen, E.S., 1935, A brief review of the geology of the San Juan region of southwestern Colorado: U.S. Geological Survey Bulletin, 843, 138 p., (incl. geologic map, scale 1:250,000), See also USGS Prof. Paper 258


[Credited to Larsen.] Tracy Creek andesite. Flows and subordinate tuff-breccia, in part andesite but chiefly tridymite dacite. In upper drainage of Tracy Creek and to northern lowest member is dense dark-gray platy andesite. To north this member consists of a number of flows with some breccia of tridymite dacite. Occurs in [Saguache County], southwestern Colorado, in extreme southern part of Saguache quadrangle but extends a short distance into Del Norte quadrangle and makes up much of drainage of Tracy Creek, for which it is named. Underlies Conejos andesite. Overlies Beidell latite-andesite irregularly. Is of pre-Potosi age. Assigned to Miocene(?).

Source: US geologic names lexicon (USGS Bull. 896, p. 2174-2175).

Map showing publication footprint
  • Usage in publication:
    • Tracy Creek Quartz Latite*
  • Modifications:
    • Age modified
  • AAPG geologic province:
    • San Juan Mountains province

For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates usage by the U.S. Geological Survey. Other usages by state geological surveys.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name does not conform with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005). This may be explained within brackets ([ ]).